Abstract: Heavily doped silver-lead titanate composite films were prepared via a sol-gel process with fresh sol and aged sol respectively. The composition and structure
of precursor sol and film were investigated by means of XRD, SEM and TEM. The results show that silver exists in the form of Ag⁺ in fresh sol while
it forms hexagonal silver clusters in aged sol. The existence state of silver in the sol directly influences the phase formation process of films. When
silver exists as Ag⁺ in the sol, the transformation of Ag⁺ to silver crystalline particles consumes a lot of Pb²⁺ to form silver-lead alloy.
In the case that silver is slightly doped, Pb²⁺ deficient pyrochlore Pb₂Ti₂O₇ phase forms because of Pb²⁺ consumed to form
silver-lead alloy; but in the case that silver is heavily doped, the formation of silver-lead alloy saturates, and surplus Ag⁺ takes the
place of deficient Pb²⁺ and silver-containing perovskite PbTiO₃ phase formed. When silver exists in the form of silver cluster in the sol,
the formation of silver crystalline phase does not consume Pb²⁺, perovskite PbTiO₃ phase is directly formed in the films.

Key words: silver, lead titanate, composite film, sol-gel process